mer-Bis(quinoline-2-carboxaldehyde 4-ethylthiosemicarbazonato)nickel(II) methanol 0.33-solvate 0.67-hydrate

The title complex exhibits a distorted octahedral geometry about the metal centre, which coordinates two tridentate ligands that are perpendicular to each other.

In the title compound, [Ni(C 13 H 13 N 4 S) 2 ]•0.33CH 3 OH•0.67H 2 O, the Ni II atom is coordinated by two tridentate quinoline-2-carboxaldehyde 4-ethylthiosemicarbazonate ligands in a distorted octahedral shape.At 100 K, the crystal symmetry is monoclinic (space group P2 1 /n).A mixture of water and methanol crystallizes with the title complex, and one of the ethyl groups in the coordinating ligands is disordered over two positions, with an occupancy ratio of 58:42.There is intermolecular hydrogen bonding between the solvent molecules and the amine and thiolate groups in the ligands.No other significant interactions are present in the crystal packing.

Structure description
Thiosemicarbazones are a type of Schiff base ligand formed by the condensation of thiosemicarbazides with carbonyl compounds (Arulmurugan et al., 2010).They commonly behave as N,S-or N,N 0 ,S-chelating agents, coordinating the metal through the imine N and S atoms.They frequently feature more than two covalent sites, the number depending on the aldehyde used during the synthesis and on the tautomeric equilibrium of the thiosemicarbazone (Latheef et al., 2021;Osman et al., 2021).The versatility of the compounds, along with their metal complexes, have attracted significant interest in the fields of chemistry and biology.They exhibit a broad spectrum of biological properties, including antibacterial, anticancer, antiproliferative and antiviral activities (Chaturvedi, 2012;Damit et al., 2021;Montalbano et al., 2023;Kumar et al., 2023;Arif et al., 2024).For instance, a series of quinoline-2-carboxaldehyde thiosemicarbazone derivatives and their Cu II and Ni II complexes have been reported by Bisceglie et al. (2015) for biological survey studies.
Ni II complexes having sulfur donors have been studied, receiving considerable attention due to the identification of a sulfur-rich coordination environment in biologically relevant nickel ompounds, such as the active sites of certain ureases, hydrogenases, as well as dehydrogenases, that may play a role in the supposed mutagenicity of nickel compounds (Latheef et al., 2021).The coordination chemistry of nickel is thus of interest with respect to its important roles in biological systems (Jayakumar et al., 2022;Sankar & Sharmila, 2023).This is due to the ability of nickel to adopt different coordination environments, such as tetrahedral, square planar and octahedral.The nickel ion can also bind to soft and hard donor ligands, which allows its coordination chemistry to encompass a variety of coordination environments, coordination numbers and oxidation states (Jayakumar et al., 2022).
The asymmetric unit of the title compound contains one complex with formula C 26 H 26 N 8 S 2 Ni and a mixture of water and methanol.The structure of the title compound is confirmed to be in a 2:1 ligand-metal complex, where the two ligands are perpendicular to each other in a distorted octahedral shape, coordinating in a meridional fashion (Fig. 1).This aligns with the methyl analogue of the complex found in the literature, which has methyl groups in place of the ethyl groups (Bisceglie et al., 2015), with its two ligands coordinating as anionic deprotonated molecules.In the structure reported herein, one of the ethyl groups is disordered over two positions, with an occupancy ratio refined as 58:42.The occupancy ratio of the solvent molecules, methanol and water, was refined to 1/3:2/3.
Each methanol/water molecule bridges two neighbouring complexes through intermolecular N4-H4� � �O(solvent) and OH(solvent)� � �S2 i hydrogen bonds (Table 1).The crystal structure is further stabilized by weaker intermolecular N8-H8� � �N3 ii hydrogen bonds, forming a tri-periodic supramolecular network (Fig. 2).No other significant interactions are present in the crystal packing of the title compound.In contrast, in the case of the methyl analogue complex, no solvent is present in the unit cell (Bisceglie et al., 2015).Furthermore, this methyl complex also features intermolecular interactions of C-H groups with the quinoline �-system, which are not observed in the structure reported herein.The Ni-N bond lengths are in good agreement with those observed in other octahedral [Ni(N,N 0 ,S) 2 ] 2+ complexes retrieved from the Cambridge Structural Database (CSD, Version 5.45; Groom et al., 2016): refcodes NOTWEA (Min et al., 2014), and JUKRAK and JUKQUD (Bisceglie et al., 2015).To the best of our knowledge, no quinoline-2-carboxaldehyde 4-ethylthiosemicarbazonate-nickel(II) complexes have been deposited in the CSD so far.
In the title compound, no H peaks were located on N3 and N7 in a difference map.Additionally, the C11 N3 and C24 N7 bond lengths are 1.3438 (19) and 1.3355 (19) A ˚, respectively, which confirms that significant double-bond character is present, and that the ligand is in its deprotonated form.Spectroscopic and mass spectrometry analyses of the complex further confirm that the 2:1 deprotonated ligandmetal complex is present.

Figure 1
The molecular structure of the title compound with the more abundant ethyl-group positions.Displacement ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity (with the exception of H4).Atoms C1S, O1S and O1W are for the disordered solvent molecules, methanol and water.The dashed bond is the intermolecular hydrogen bond between the complex and the methanol molecule (Table 1, entry 2).

Figure 2
Perspective view of the crystal packing of the title compound approximately along the b axis.Solvent molecules and H atoms have been omitted for clarity.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.One ethyl group (C25-C26) was modelled for disorder over two parts.Displacement parameters for this group were restrained to be similar and site occupancies were refined to 0.58 (2) and 0.42 (2).The last residual peaks in the difference maps were modelled as a mixture of water and methanol sharing a single site, and displacement parameters for these atoms (C1A, O1A and O1W) were constrained to be identical.Occupancies for water and methanol were refined to 0.672 (6) and 0.328 (6), respectively.The H atoms of the solvent molecules could not be located from a difference map and were thus placed in calculated positions.The H atoms of the amine groups (H4 and H8) were refined freely (positions and isotropic displacement parameters), while other H atoms were placed in calculated positions.(Bruker, 2016), SHELXT2018 (Sheldrick, 2015a), SHELXL2019 (Sheldrick, 2015b), Mercury (Macrae et al., 2020) and publCIF (Westrip, 2010).

Table 2
Experimental details.
Computer programs: APEX4 and SAINT